There have been conventionally known various substrate process systems for subjecting substrates such as semiconductor wafers to a cleaning process, a heating process, and so on.
Referring to FIGS. 14 and 15, an example of such a conventional substrate process system is described. FIG. 14 is a schematic side view showing a structure of the conventional substrate process system, and FIG. 15 is a sectional view of the substrate process system shown in FIG. 14 taken along the line E-E.
As shown in FIGS. 14 and 15, the conventional substrate process system 70 includes a carrier station 70a and a process station 70b adjacent to the carrier station 70a. In the carrier station 70a, a semiconductor wafer W (hereafter also referred to as “wafer W”) which is not processed yet and/or the wafer W which has been already processed are placed. In the process station 70b, the wafer W is subjected to a cleaning process and a heating process succeeding the cleaning process. The carrier station 70a includes a FOUP (Front opening Unified Pod, wafer storage pod) 20 capable of containing a plurality of, e.g., twenty-five wafers W which are horizontally arranged at predetermined vertical intervals, and a stage 25 on which a plurality of, e.g., four FOUPs 20 can be placed in parallel. The process station 70b includes a transit unit (TRS; Transit Station) 30 in which the wafer W transferred from the FOUP 20 is temporarily placed, and a plurality of, e.g., four process chambers (SPIN) 40 of a spin-type to which the wafer W temporarily placed in the transit unit 30 is transferred (FIG. 14 shows only two of the four process chambers 40). In the process chambers 40, the wafer W is subjected to a cleaning process, a drying process, and so on.
In the carrier station 70a, there is disposed a first wafer transfer apparatus (CRA) 80 which can move to transfer the wafer W between the FOUP 20 and the transit unit 30. Similarly, in the process station 70b, there is disposed a second wafer transfer apparatus (PRA) 60 which can move to transfer the wafer W between the transit unit 30 and the process chamber 40.
The first wafer transfer apparatus 80 to be used for transferring the wafer W between the FOUP 20 and the transit unit 30 is described in detail below.
The first wafer transfer apparatus 80 includes a base member 81 which runs along a rail (not shown) extending in the Y direction in FIG. 15, and a vertical moving mechanism 82 disposed on an upper surface of the base member 81, the vertical moving mechanism 82 being elongatable and compressible in the Z direction. A support base 85 is disposed on an upper part of the vertical moving mechanism 82. A fork support member 83 is fixed to the support base 85. A fork 84 for holding the wafer W is supported by the fork support member 83.
As shown in FIG. 15, the vertical moving mechanism 82 can rotate in the θ direction relative to the base member 81. Namely, the support base 85 can move in the Y direction and the Z direction, and rotates in the θ direction. The fork 84 is disposed above the support base 85. The fork support member 83 has a horizontal moving mechanism (not shown) which is fixed on a proximal end of the fork 84. Thus, the fork 84 can be moved in the X direction in FIGS. 14 and 15 by the horizontal moving mechanism.
How the wafer W is taken out from the FOUP 20 by the fork 84 is described. The fork 84 is moved at first to a pre-unloading position which is a position below the wafer W to be taken out, and then the support base 85 is moved upward to move the fork 84 upward by a predetermined distance from the pre-unloading position. In the course of the upward movement of the fork 84, the fork 84 lifts the wafer W contained in the FOUP 20, so that the wafer W is transferred to an upper surface of the fork 84.
In order to sequentially, continuously process the plurality of wafers W in the process chamber 40, the wafers W contained in the FOUP 20 should be sequentially transferred to the transit unit 30. However, the first wafer transfer apparatus 80 has only one fork 84. Thus, when the plurality of wafers W contained in the FOUP 20 are sequentially transferred to the transit unit 30, a series of steps has to be repeated in which the wafer transfer apparatus 80 moves near the FOUP 20 at first, then the fork 84 takes out one wafer W from the FOUP 20 and holds the same, the first wafer transfer apparatus 80 then moves near the transit unit 30, and thereafter the fork 84 holding the wafer W delivers the wafer W to the transit unit 30.
However, these steps for sequentially transferring the plurality of wafers W contained in the FOUP 20 require a lot of time, which degrades a general processing capability of the substrate process system 70.
Another known wafer transfer apparatus includes a plurality of forks that simultaneously moves horizontally forward, upward or downward, and then horizontally rearward, as disclosed in JP9-270450A, for example. With the use of the wafer transfer apparatus disclosed in JP9-270450A, it is possible to take out a plurality of wafers W from the FOUP, and to collectively send the wafers W to the transit unit by means of the plurality of forks. However, this method is actually difficult to carry out. The reason is as follows.
In the general substrate process system, a distance between the adjacent wafers W of 300 mm in diameter contained in the FOUP is determined to be about 10 mm by a standard or the like, and this distance between the wafers W cannot be varied in the FOUP. The pre-unloading position on which the wafer W is taken out from the FOUP is set at a predetermined position based on a structure of the FOUP.
Meanwhile, a distance between the forks for transferring the wafers W from the FOUP to the transit unit must be equal to the distance between the wafers W contained in the FOUP. In addition, it is generally necessary to design a distance between the wafers W, when the wafers W are received in the transit unit, is equal to the distance between the wafers contained in the FOUP.
However, it is sometimes difficult in terms of design to conform, to the distance between the wafers W in the transit unit, a distance between forks in the second wafer transfer apparatus (wafer transfer apparatus 60 in FIG. 15) for carrying the wafers W between the transit unit and the process chamber. This is because the second wafer transfer apparatus which carries out the wafers W from the transit unit is required to operate at a speed higher than that of the first wafer transfer apparatus, in order that the second wafer transfer apparatus accesses the plurality of process chambers. Thus, the fork for holding the wafer W of the second wafer transfer apparatus is needed to have a strength larger than that of the fork of the first wafer transfer apparatus. For this reason, the fork of the second wafer transfer apparatus has an enlarged thickness. Thus, a distance between the wafers W in the transit unit to which the second wafer transfer apparatus comes close must be enlarged. In addition, when the plurality of wafers W are simultaneously taken out from the FOUP by the plurality of forks, the wafers W corresponding to the forks are taken out from above or from below of the FOUP. In this case, when it is necessary to take every other wafer W in the FOUP depending on a process, such a structure is disadvantageous.